Add linting of YAML files

[wwarriner]

Pull Request

Overview

Adds linting of YAML files to pre-commit hooks and to CI check step. Sorry, there isn't a good method to get real-time linting in VSCode yet.

This should help reduce issues with unintentional changes to YAML files.

Proposed Changes

• Adds yamllint to build environment.
• Adds yamllint to pre-commit hooks.
• Adds yamllint to CI check step.
• Adds .yamllint.yaml config file.
• Updates YAML files to comply with .yamllint.yaml configuration file.

Related Issues

Fixes #747

[bdu-birhanu]

Everything looks great on my end!
I tested it on my local system, and it works well, except for an entry line in the pre-commit-config.yaml under hooks, as noted below.